The ripples from the VW cheating scandal have spread far these last two weeks, and the fallout isn’t over yet. According to a new study from the Department of Energy’s Oak Ridge National Laboratory, a significant gap exists between the mileage American cars demonstrate during federal testing and the mileage they actually get during road conditions. And, researchers warn, that gap has widened.The study found that engine efficiency in U.S. cars was overestimated by roughly 15 percent from the 1990s into the 2000s, but that over the last three years that same metric was off by between 23 and 25 percent. In other words, the newest cars on the road could be providing consumers around a quarter less mileage than their manufacturers—and federal regulators—claim.This isn’t just a story of false advertising; lower gas mileage means higher greenhouse gas emissions and more local pollutants. Reuters cites a study released two years ago by the International Council on Clean Transportation, in which researchers found that the gap between cars’ emissions on the test track and those on the actual road more than quadrupled from 8 percent in 2001 to 38 percent in 2013.It seems Volkswagen owners aren’t the only ones out there being duped.